I'm converting an AIFF to FLAC. Most of the metadata gets correctly transferred, but certain pieces are not.

Missing metadata:
  • Grouping
  • BPM
  • Remixer
  • Release Time
  • Official Audio File Webpage
  • Publishers' Official Webpage

Things that are correctly copied:
  • Title
  • Artist
  • Album
  • Year
  • Track
  • Album Art

Any idea what may be causing this and what can be done? I did some Googling and I don't think there are any DSP processors that can address this.